Transmit adaptive equalization using ordered sets

ABSTRACT

In a communication system comprising first and second nodes, a transmit adaptive equalization technique is implemented utilizing ordered sets. The first and second nodes may communicate over a Fibre Channel link or other medium. The first and second nodes comprise respective transmitter and receiver pairs, with the transmitter of the first node configured for communication with the receiver of the second node and the receiver of the first node configured for communication with the transmitter of the second node. The first node is operative to receive from the second node information specifying an adjustment to one or more equalization parameters of the first node. The information is received in designated portions of one or more ordered sets transmitted from the second node to the first node in conjunction with initialization of a communication link between the first and second nodes. The first node adjusts the equalization parameter(s) in accordance with the received information.

FIELD OF THE INVENTION

The present invention relates generally to communication systems, andmore particularly to equalization techniques for use in communicationssystems comprising, by way of example, one or more Fibre Channel linksor other serial data channels.

BACKGROUND OF THE INVENTION

As is well known, Fibre Channel (FC) is an American National StandardsInstitute (ANSI) standard specifying a bidirectional serial datachannel, structured for high performance capability. Physically, theFibre Channel may be viewed as an interconnection of multiplecommunication points, called N_Ports, interconnected by a linkcomprising a switching network, called a fabric, or a point-to-pointlink. Fibre is a general term used to cover all physical media typessupported by the Fibre Channel, such as optical fibre, twisted pair, andcoaxial cable.

The Fibre Channel provides a general transport vehicle for Upper LevelProtocols (ULPs) such as Intelligent Peripheral Interface (IPI) andSmall Computer System Interface (SCSI) command sets, High-PerformanceParallel Interface (HIPPI) data framing, IP (Internet Protocol), IEEE802.2, and others. Proprietary and other command sets may also use andshare the Fibre Channel, but such use is not defined as part of theFibre Channel standard.

Fibre Channel is structured as a set of hierarchical functions denotedFC-0, FC-1, FC-2, FC-3 and FC-4.

FC-0 defines the physical portions of the Fibre Channel including thefibre, connectors, and optical and electrical parameters for a varietyof data rates and physical media. Coax and twisted pair versions aredefined for limited distance applications. FC-0 provides thepoint-to-point physical portion of the Fibre Channel. A variety ofphysical media is supported to address variations in cable plants.

FC-1 defines the transmission protocol which includes the serialencoding, decoding, and error control.

FC-2 defines the signaling protocol which includes the frame structureand byte sequences.

FC-3 defines a set of services which are common across multiple ports ofa node.

FC-4 is the highest level in the Fibre Channel standard. It defines themapping, between the lower levels of the Fibre Channel and the IPI andSCSI command sets, the HIPPI data framing, IP, and other ULPs.

Additional details regarding these and other aspects of Fibre Channelcan be found in the ANSI Fibre Channel standard documents, including theFC-PH, FC-FS, FC-AL-2, FC-PI, FC-DA, FC-MI and FC-LS documents, all ofwhich are incorporated by reference herein.

In typical conventional practice, Fibre Channel links are designed tooperate at data rates of 4.25 Gbps, 2.125 Gbps or 1.0625 Gbps. Althoughhigher data rates are possible, the industry is reluctant to spend moneyupgrading existing hardware to implement these higher data rates. Theproblem is that as data rates increase, to the proposed Fibre Channelrates of 8 Gbps, 16 Gbps and higher, the existing hardware degrades theelectrical signals to the extent that error-free operation cannot beachieved without electrical equalization.

Current implementations generally attempt to address this problemthrough the use of pure receive equalization. However, at high datarates, on the order of 8 Gbps or higher, this receive-only equalizationapproach is very complicated, and requires significant increases in sizeand power consumption for the associated hardware. Moreover, thereceive-only equalization approach may fail to provide desired levels ofperformance at the high data rates.

Accordingly, what is needed is an improved approach to equalization forFibre Channel or other serial data channels, which can accommodatehigher data rates without the need for hardware infrastructure upgradeswhile also avoiding the drawbacks of conventional receive-onlyequalization.

SUMMARY OF THE INVENTION

The present invention provides techniques for transmit adaptiveequalization that overcome one or more of the drawbacks of conventionalpractice.

In accordance with one aspect of the invention, a transmit adaptiveequalization technique is implemented in a communication systemcomprising first and second nodes. The first and second nodes maycommunicate over a Fibre Channel link or other medium. The first andsecond nodes comprise respective transmitter and receiver pairs, withthe transmitter of the first node configured for communication with thereceiver of the second node and the receiver of the first nodeconfigured for communication with the transmitter of the second node.The first node is operative to receive from the second node informationspecifying an adjustment to one or more equalization parameters of thefirst node. The information is received in designated portions of one ormore ordered sets transmitted from the second node to the first node inconjunction with initialization of a communication link between thefirst and second nodes. The first node adjusts the one or moreequalization parameters in accordance with the received information.

In a similar manner, the second node may also adjust one or more of itsequalization parameters in accordance with information received indesignated portions of one or more ordered sets transmitted from thefirst node to the second node in conjunction with initialization of thecommunication link between the first and second nodes. Thus,substantially simultaneous transmit adaptive equalization may beprovided for both the first node and the second node, utilizing aplurality of ordered sets transmitted between the first and second nodesin conjunction with initialization of a communication link between thosenodes.

In an illustrative embodiment, the ordered sets may comprise trainingordered sets transmitted between the first and second nodes, forexample, during a speed negotiation process carried out between thefirst and second nodes in conjunction with initialization of thecommunication link, or at another suitable time during or afterinitialization of the link.

Each of the training ordered sets in the illustrative embodimentcomprises both a training pattern and equalization parameter adjustmentinformation. For example, a training ordered set transmitted from thefirst node to the second node may comprise a training pattern that isused by the second node to determine equalization parameter adjustmentinformation for the first node. This training ordered set may alsocomprise equalization parameter adjustment information for the secondnode, as determined by the first node. Similarly, a training ordered settransmitted from the second node to the first node may comprise atraining pattern that is used by the first node to determineequalization parameter adjustment information for the second node. Thistraining ordered set may also comprise equalization parameter adjustmentinformation for the first node, as determined by the second node.

In the above-noted embodiment, data portions of a given training orderedset that are used to convey equalization parameter adjustmentinformation may also comprise at least a portion of a training pattern.However, it should be noted that, in alternative embodiments, signalsother than the training pattern of an ordered set may be used inevaluating signal quality at the receiver of a given node.

The training ordered sets are preferably transmitted in place of one ormore conventional ordered sets which would otherwise be transmittedbetween the first and second nodes during the speed negotiation process,or at another suitable time during or after initialization of the link.The training ordered sets may also be configured to communicate statusindicators for the transmit adaptive equalization process, such as “inprocess” and “completed” indicators.

The equalization parameters to be adjusted may comprise a plurality oftap coefficients of a finite impulse response (FIR) filter associatedwith the corresponding node. The information specifying an adjustment tothe equalization parameters in this example may comprise, for aparticular one of the plurality of coefficients, at least one of anincrement coefficient action, a decrement coefficient action, and a holdcoefficient action.

In accordance with another aspect of the invention, a proxy mechanismmay be used to transmit information between the first and second nodes.For example, such a proxy mechanism may be used to transmit theequalization parameter adjustment information over at least oneadditional interface other than those associated with first and secondends of the communication link.

Advantageously, the present invention in the illustrative embodimentsprovides improved responsiveness to variations in channel properties dueto temperature, humidity or other environmental factors. Equalizationparameter adjustment is provided in a manner that is highly adaptive tosuch environmental variations.

The illustrative embodiments provide a number of other significantadvantages over the conventional techniques previously described. Forexample, the illustrative embodiments can accommodate higher FibreChannel data rates, such as 8 Gbps, 16 Gps and higher, without the needfor hardware infrastructure upgrades. In addition, substantiallyimproved performance relative to conventional receive-only equalizationis provided, with minimal impact to existing protocols of the FibreChannel standard. Furthermore, the transceiver hardware area and powerconsumption required for equalization are considerably reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are simplified block diagrams showing exemplary FibreChannel communication systems in which the present invention isimplemented.

FIG. 3 shows an exemplary training ordered set (TOS) format suitable foruse in performance of transmit adaptive equalization in accordance withan illustrative embodiment of the invention.

FIG. 4 is a diagram illustrating the manner in which filter coefficientsmay be controlled in a transmit adaptive equalization using a TOS formatsuch as that of FIG. 3.

FIG. 5 is a flow diagram illustrating one possible implementation oftransmit adaptive equalization using the TOS approach of FIGS. 3 and 4.

FIGS. 6 and 7 show additional examples of transmit adaptive equalizationperformed in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention will be illustrated herein in conjunction with exemplarycommunication systems comprising one or more bidirectionalpoint-to-point serial data channels configured in accordance with theANSI Fibre Channel standard. It should be understood, however, that theinvention is more generally applicable to any system comprising one ormore serial data channels in which it is desirable to provide improvedequalization so as to facilitate operation at high data rates. Forexample, the described techniques can be adapted in a straightforwardmanner to other single-lane or multi-lane serial links including, butnot limited to, Infini-Band, IEEE 1394, PCI-Express, Ethernet, andcertain DWDM or SONET links.

FIG. 1 shows a portion of a communication system 100 in which thepresent invention is implemented. The system 100 comprises a first node102, also denoted as Node A, and a second node 104, also denoted as NodeB. The two nodes are connected by a bidirectional serial data channeltransmission medium 105, also referred to herein as a “link.” Node Acomprises a transmitter 102T configured for communication with areceiver 104R of Node B, and a receiver 102R configured forcommunication with a transmitter 104T of Node B.

By way of example, Node B in FIG. 1 may be configured as a backplanewhich connects two switch ASICs implementing E_Ports, not explicitlyshown in the figure. Such elements may support multiple data rates, suchas, for example, data rates of 4, 8, 10 and 16 Gbps.

FIG. 2 shows a more detailed view of one possible alternative topologyof a system 100′ comprising Node A and Node B. In this arrangement, NodeB is again configured as a backplane, but this time comprises a SwitchOn Chip (SOC) element 110 with point-to-point connections to a pluralityof NL_Ports or FL_Ports 112 that may be, for example, Fibre Channel HardDisk Drives (HDDs). Like the NL_Ports in the FIG. 1 example mentionedpreviously, the elements 112 in this example may support multiple datarates, such as the above-noted data rates of 4, 8, 10 and 16 Gbps.

In both FIG. 1 and FIG. 2, the Node B transceivers are illustrativelypart of a backplane that is comprised of NL_Ports or FL_Ports. However,the invention is applicable to other types of ports, such as N_Ports,E_Ports and F_Ports on a backplane, or within a fabric, as defined inthe above-cited documents of the Fibre Channel standard.

It is to be appreciated that the particular numbers of nodes shown inFIGS. 1 and 2, and their particular topology and configuration, arepresented by way of illustrative example only. Other embodiments of theinvention can include different numbers and arrangements of nodes. Forexample, various topologies based on fabric interconnection of the nodesare possible. The invention is also applicable to topologies such asthose described in the above-cited FC-DA document of the Fibre Channelstandard, as well as other Fibre Channel topologies.

The present invention in the illustrative embodiments provides transmitadaptive equalization in a Fibre Channel system such as system 100 ofFIG. 1 or system 100′ of FIG. 2.

Generally, a first node, which may be Node A or Node B, is operative toreceive from the other node, referred to as a second node, informationspecifying an adjustment to one or more equalization parameters of thefirst node. The information is received in designated portions of one ormore ordered sets transmitted from the second node to the first node inconjunction with initialization of a communication link between thefirst and second nodes. The equalization parameter(s) of the first nodeare then adjusted in accordance with the received information. Forexample, the equalization parameters may comprise a plurality of tapcoefficients of a finite impulse response (FIR) filter associated withthe transmitter of the first node, as will be described in greaterdetail below in conjunction with FIG. 4. Other filter or transformmechanisms may be used to provide the desired equalizationfunctionality. More generally, any appropriate mathematical transformcharacterized by one or more equalization parameters may be used.

Thus, the invention in the illustrative embodiments provides feedbackmechanisms which utilize modified ordered sets, each referred to hereinas a training ordered set (TOS), to communicate training patterns andequalization parameter adjustment information between transmitting andreceiving nodes.

A given TOS in the illustrative embodiments comprises, in addition tothe equalization parameter adjustment information for the node thatreceives the TOS, a training pattern that is used by the receiving nodein evaluating received signal quality and determining equalizationadjustment information for the other node. This allows substantiallysimultaneous transmit adaptive equalization to be provided for both thefirst node and the second node, utilizing a plurality of ordered setstransmitted between the first and second nodes.

Each of the training ordered sets in the illustrative embodiments thuscomprises both a training pattern and equalization parameter adjustmentinformation. For example, a training ordered set transmitted from thefirst node to the second node may comprise a training pattern that isused by the second node to determine equalization parameter adjustmentinformation for the first node. This training ordered set may alsocomprise equalization parameter adjustment information for the secondnode, as determined by the first node. Similarly, a training ordered settransmitted from the second node to the first node may comprise atraining pattern that is used by the first node to determineequalization parameter adjustment information for the second node. Thistraining ordered set may also comprise equalization parameter adjustmentinformation for the first node, as determined by the second node.

It is to be appreciated that signals other than the training pattern ofan ordered set may be used in evaluating signal quality at the receiverof a given node.

The equalization parameter adjustment process may be repeatediteratively, until the both the first and second nodes arrive at sets ofequalization parameters which provide a desired signal quality at theirrespective receivers.

An advantage of the TOS approach of the illustrative embodiments is thatit can be implemented during an otherwise conventional speed negotiationprocess carried out between the first node and the second node inconjunction with initialization of a Fibre Channel link between thenodes. This allows the speed negotiation and transmit adaptiveequalization to be carried out substantially simultaneously with oneanother in conjunction with initialization of the Fibre Channel link, ina manner compliant with the Fibre Channel standard. Thus, theillustrative embodiments are readily interoperative with legacy systems.

Currently, no mechanism exists in the Fibre Channel standard that allowsa receiving node to direct a transmitting node to perform transmitadaptive equalization so as to overcome signal degradation at thereceiver. The TOS approach of the illustrative embodiments provides theneeded dynamic feedback mechanism for supporting the performance oftransmit adaptive equalization in a Fibre Channel system.

In operation, a receiving node evaluates the quality of a signaltransmitted by the transmitting node. As indicated above, this signalquality evaluation may be facilitated using a training patterntransmitted from a transmitting node in a TOS. Other signal qualityevaluation techniques may be used. Assume the transmitting and receivingnodes are Node A and Node B, respectively, of the example systems shownin FIGS. 1 and 2. Thus, Node B evaluates the quality of a signaltransmitted by Node A during the speed negotiation process, preferablyusing a training pattern in a TOS received from Node A. Following theevaluation of the received signal quality, the transmitter of Node Bsends a command to the receiver of Node A requesting an adjustment ofthe equalization parameters of the transmitter of Node A. This commandis preferably transmitted in a TOS sent from Node B to Node A. Node Amakes the requested adjustment and transmits the training pattern inanother TOS, using the adjusted equalization parameters. This iterativeprocess continues until Node A converges upon suitable equalizationparameter values providing a desired signal quality at the receiver ofNode B. The iterative process thus converges to a set of equalizationparameters leading to the desired signal quality at the Node B receiver.

Of course, the roles of Node A and Node B can be reversed to implement asimilar and substantially simultaneous transmit adaptive equalizationprocess for transmission in the opposite direction, that is, with Node Bas the transmitting node for which equalization parameters are adjustedresponsive to received signal quality determinations at Node A. Asmentioned previously, this allows substantially simultaneous transmitadaptive equalization to be provided for both Node A and Node B,utilizing a plurality of ordered sets transmitted between these nodes.

A conventional speed negotiation process carried out between Node A andNode B in the systems of FIGS. 1 and 2 will generally involvetransmission of Not Operational State (NOS) and Offline State (OLS)ordered sets for a specified time duration defined in Fibre Channeldocuments cited above. These ordered sets are transmitted encoded infour 10-bit characters by the transmitting node link layer and decodedto 8-bit characters by the link layer of the receiving node.

A given TOS as described above may be utilized to perform transmitadaptive equalization during the speed negotiation process between NodeA and Node B. In such an arrangement, the TOS is preferably transmittedduring speed negotiation, in place of the NOS and OLS ordered sets usedin conventional practice.

The transmit adaptive equalization process may take place at anyconvenient time, during or after the initialization of a communicationlink, but in the illustrative embodiments takes place during the speednegotiation. If signal quality degradation conditions are laterdetected, for example, due to modifications in the data path, theprocess can be executed again for a given link without performing speednegotiation.

FIG. 3 shows one possible example of a TOS format utilizable in theillustrative embodiments. The TOS format in this example includes firstand second ordered sets denoted TOS1 and TOS2. Each ordered setcomprises four characters, with each character being 8 bits in lengthprior to encoding and 10 bits in length after encoding. The firstcharacter of each ordered set in this example is the K28.5 controlcharacter, and the remaining characters comprise data portions. Morespecifically, the TOS1 ordered set comprises the K28.5 control characterfollowed by data portions D1, D2 and D3, while the TOS2 ordered setcomprises the K28.5 control character followed by data portions D4, D5and D6. Thus, each of the ordered sets TOS1 and TOS2 is 32 bits inlength prior to encoding, and 40 bits in length after encoding.

As will be described below, the illustrative embodiments utilize two ofthe data portions D1, D2, D3, D4, D5 and D6 to transmit from Node B toNode A information specifying an adjustment to one or more equalizationparameters of Node A. More specifically, data portions D5 and D6 areutilized, for a total of 16 bits prior to encoding, to convey theequalization parameter adjustment commands from Node B to Node A. Thecontrol characters and data portions of TOS1 and TOS2 also comprise theabove-mentioned training pattern, used by a receiving node to evaluatesignal quality.

Thus, this exemplary TOS format comprises both equalization parameteradjustment information and one or more training patterns. The dataportions of TOS1 and TOS2 that are used for equalization parameteradjustment may also be used as part of the training pattern, but this isnot a requirement of the invention.

It should be noted that, for Fibre Channel, the data portions D1 and D4of TOS1 and TOS2 in the illustrative embodiments cannot take on thefollowing predefined values, because those values are reserved for otherFibre Channel functions:

D5.4 (CLS)

D9.0 (LPB)

D9.2 (LR)

D10.4 (EOF/SOF)

D10.5 (EOF/SOF)

D17.4 (Full Dplx)

D20.4 (ARB)

D5.0 (LPE)

D21.0 (LIP)

D21.1 (OLS)

D21.2 (NOS)

D21.4 (EOF/SOF)

D21.5 (SOF/EOF)

D21.7 (VC_RDY)

D31.3 (CLK SYNC X)

D31.5 (CLK SYNC Y)

D31.6 (CLK SYNC Z)

D31.2 (MARK)

FIG. 4 shows the manner in which data portions D5 and D6 of TOS2 areutilized to carry information specifying adjustments to one or moreequalization parameters of a given node. The two data portions D5 and D6are treated as a single 16-bit command structure organized in the mannershown in the figure.

In the FIG. 4 example, the first fourteen bits of the 16-bit commandstructure comprise coefficient update bits (bits 1 to 14), also referredto as “Action” bits. In the coefficient update bits, there are two bitsfor each of seven coefficients. The seven coefficients, each of whichcorresponds to a tap of an FIR filter, are denoted C1, C2, C3, C4, C5,C6 and C7. For each of the coefficients, a corresponding action isencoded using the associated pair of bits. The possible actions in thisexample include Hold, Decrement, and Increment, encoded by bit pairs 00,01, and 10, respectively. In the case of a given Hold action, alsoreferred to as a No Change action, the corresponding coefficient remainsunchanged, while for Decrement or Increment actions, the correspondingcoefficients are adjusted downward or upward, respectively, by adesignated amount. The particular amount of the adjustment willtypically depend on implementation-specific factors, such as the type ofequalization algorithm being used, and numerous suitable arrangementswill be readily apparent to those skilled in the art. Other encodings oftransmit parameters may be used depending on the choice of transmitadaptive equalization mechanism and the operations that may beconvenient to apply to the present equalization parameter values.

The final two bits (bits 15 and 16) of the 16-bit command structure inFIG. 4 are used to convey additional information, including “in process”and “completed” status indicators for the transmit adaptive equalizationprocess. This allows TOS values containing no information to be passedif there are latencies in coefficient value calculation or differencesin convergence rate between the two ends of a link.

The transmit adaptive equalization process may be considered completefor a given node, e.g., Node A, when the coefficient update bits foreach of the coefficients are set to the Hold value (00), and bits 15 and16 are set to the Completed value (01). This indicates that optimumcoefficients have been established for all filter taps, and that Node Ais to hold these values until otherwise instructed by Node B. The Holdvalue may be set even in the absence of perfect convergence when thereceiver has detected that an adequate approximation to perfectconvergence has been achieved. Such cases may occur when, after acertain amount of time, the receiver has been unable to improve upon thetransmitter behavior, for example, because the transmitter parametersare cycling near an optimum or because the transmitter does not have anoperational transmit equalization circuit.

The FIG. 4 example supports parallel update of transmitter FIRcoefficients to a maximum of seven taps, although the technique can beadapted in a straightforward manner to handle more or fewer taps. It isnot necessary for a given implementation to support all of the taps thatcan be accommodated by the command format. The technique does notrequire any particular tap weight resolution, and is tolerant ofcorrupted or lost coefficient updates. Actions applied to unsupportedtaps are ignored.

It should be understood that the particular TOS format and commandstructure shown in FIGS. 3 and 4 are presented by way of illustrativeexample only, and numerous alternative arrangements may be used. Theparticular TOS format and command structure selected for use in a givenembodiment may depend upon factors such as the requirements of theparticular serial link or other serial data channel being implemented.As another example, it is possible to utilize a TOS format whichincludes more or fewer that the two ordered sets TOS1 and TOS2 shown inthe FIG. 3 example, or an ordered set comprising more or fewer than thetwo bytes used in the FIG. 4 example.

As noted above, data portions D5 and D6 of TOS2 are used in theillustrative embodiments to convey the coefficient adjustmentinformation. The K28.5 control characters and all data portions,including those data portions used to convey coefficient adjustmentinformation, may be used as training patterns for evaluation of receivedsignal quality. The data portions in the illustrative embodiments aredesigned to be DC balanced and to comprise valid 8b10b data charactersas defined in the Fibre Channel standard. In other embodiments, the dataportions may be designed to exhibit other characteristics suitable forfacilitating the received signal quality determination.

During the speed negotiation process, the NOS and OLS ordered sets whichwould otherwise be transmitted in conventional practice are replacedwith the TOS ordered sets as described above in order to performtransmit adaptive equalization. The two ordered sets TOS1 and TOS2 arepreferably treated as comprising a single atomic operation by thetransmitting and receiving nodes. Transmission of these two ordered setsis repeated for the time duration of the speed negotiation process.

FIG. 5 is a flow diagram illustrating transmit adaptive equalizationusing the TOS ordered sets described above. In this example, each ofNode A and Node B of system 100 or 100′ is separated into a link layerportion and a physical layer (PHY) portion of the Fibre Channel standardas indicated. As noted previously, the transmit adaptive equalization iscarried out during speed negotiation, and thus prior to theestablishment of an operational Fibre Channel link between Node A andNode B.

In step 500, Node A will set default tap levels on power up. Nodes A andB are also initialized with preliminary receive equalization parameters.These default and preliminary settings will provide sufficient signalquality to allow performance of the adaptive equalization process usingthe TOS ordered sets.

Then, as indicated at 502, the TOS ordered sets TOS1 and TOS2 aretransmitted from transmitter 102T of Node A to receiver 104R of Node Bduring speed negotiation. The receiver 104R of Node B will evaluatesignal quality using the training patterns, and will determine in step504 if an equalization adjustment is required. If an adjustment is notrequired, a decision is made in step 506 to hold the coefficients attheir current values. If an adjustment is required, a determination ismade in step 508 to adjust the coefficients, and the D5 and D6 dataportions of TOS2 are adjusted in step 510 in accordance with the FIG. 4command structure to convey the coefficient adjustment commands fromtransmitter 104T of Node B to receiver 102R of Node A.

In step 512, Node A processes the received TOS in its link layerportion, and in step 514 the link layer portion sends a message to thephysical layer portion specifying the requested equalization adjustment.The equalization adjustment is then completed by the physical layerportion of Node A in accordance with the specified TOS actions, asindicated in step 516.

The monitoring of received signal quality and adjustment of equalizationparameters may be repeated until a desired received signal quality isachieved at the receiver 104R of Node B. The granularity of adjustmentand the magnitude of change for each iteration should be selected toassure stability in the convergence to the desired received signalquality levels. As described previously, the transmit adaptiveequalization process may be considered complete when the coefficientupdate bits for each of the supported coefficients are set to the Holdvalue (00), and bits 15 and 16 are set to the Completed value (01).

Although FIG. 5 illustrates the adjustment of equalization parameters ofNode A using information transmitted from Node B, similar adjustment canbe implemented in the opposite direction at substantially the same time,as in the FIG. 6 example to be described below.

Of course, the particular process steps of FIG. 5 may be altered inother embodiments of the invention.

It should be noted that the transmit adaptive equalization as describedherein can be implemented in conjunction with otherwise conventionalreceive equalization.

As noted previously, the TOS ordered sets may be used to performtransmit adaptive equalization at Node B as well as at Node A. Anexample of an arrangement of this type is illustrated in FIG. 6, whichshows TOS ordered sets being transmitted from Node A to Node B for usein generating coefficient adjustment commands which are sent from Node Bback to Node A, to provide transmit adaptive equalization at Node A asin the FIG. 5 example. However, FIG. 6 further shows TOS ordered setsbeing transmitted from Node B to Node A for use in generatingcoefficient adjustment commands which are sent from Node A back to NodeB so as to provide transmit adaptive equalization at Node B. Thus, theTOS approach can be used to provide substantially simultaneous transmitadaptive equalization for both Node A and Node B during a speednegotiation process between Node A and Node B.

FIG. 7 shows an arrangement in which a proxy mechanism is utilized inperforming transmit adaptive equalization for Nodes A and B. A system700 comprises Nodes A and B as previously described and an additionalnode, denoted Node C. Node B is coupled between Node A and Node C asshown. Node C comprises receiver 702R and transmitter 702T. Node B inthis embodiment comprises an additional transceiver includingtransmitter 704T, which communicates with receiver 702R of Node C, andreceiver 704R, which communicates with transmitter 702T of Node C.

This arrangement is an example of one in which the adaptive equalizationinformation sent in the TOS ordered sets is transmitted by additionalinterfaces other than those associated with the link being optimized.Numerous other arrangements, involving three or more nodes, may beconfigured in a straightforward manner.

The FIG. 7 example assumes Node A and B reside within a single systemand have out-of-band communication capability. The example furtherassumes that Node C is remote and has only TOS communication capabilityto Node A. As indicated in the figure, proxy information is used for thefollowing operations:

1. Adjusting filter coefficients of Node A transmitter 102T based oninformation detected by Node B receiver 104R.

2. Adjusting filter coefficients of Node B transmitter 704T based oninformation detected by Node C receiver 702R, transmitted using TOS toNode A and forwarded out-of-band to Node B.

3. Adjusting filter coefficients of Node C transmitter 702T based oninformation detected by Node B receiver 704R, transmitted out-of-band toNode A and forwarded using TOS to Node C.

4. Adjusting filter coefficients of Node B transmitter 104T usinginformation detected by Node A receiver 102R, and transmittedout-of-band to Node B.

The numerical ordering of the operations in the foregoing list shouldnot be construed as a requirement that the operations be performed inany particular order. Thus, the order in which the operations may beperformed can vary from the above-listed order. Also, alternative oradditional operations may be used, depending upon the requirements of agiven embodiment.

Advantageously, the present invention in the illustrative embodimentsdescribed above can accommodate higher Fibre Channel data rates, such as8 Gbps, 16 Gps and higher, without the need for hardware infrastructureupgrades. In addition, substantially improved performance relative toconventional receive-only equalization is provided, with minimal impactto the existing protocols of the Fibre Channel standard. Furthermore,the transceiver hardware area and power consumption required forequalization are considerably reduced.

Other advantages associated with the illustrative embodiments includethe fact that the equalization process can be used to optimize thetransmit equalization settings for both nodes. Also, because thetransmit adaptive equalization is performed in conjunction with speednegotiation between the nodes, no changes in the timing of relevantevents are required. The invention also provides a “plug and play”capability in that a given system can be configured to automaticallynegotiate the proper equalization parameters for any channel withoutuser intervention.

A further significant advantage of the illustrative embodiments is thatthey provide improved responsiveness to variations in channel propertiesdue to temperature, humidity or other environmental factors.

The present invention may be implemented in the form of one or moreintegrated circuits. For example, a given system node in accordance withthe invention may be implemented as one or more integrated circuitscomprising at least one processor and at least one memory. Numerousother configurations are possible.

In such an integrated circuit implementation, a plurality of identicaldie are typically formed in a repeated pattern on a surface of asemiconductor wafer. Each die includes a device described herein, andmay include other structures or circuits. The individual die are cut ordiced from the wafer, then packaged as an integrated circuit. Oneskilled in the art would know how to dice wafers and package die toproduce integrated circuits. Integrated circuits so manufactured areconsidered part of this invention.

The present invention may also be implemented at least in part in theform of one or more software programs that, within a given node, arestored in memory and run on a processor. Such node processor and memoryelements may comprise one or more integrated circuits.

Again, it should be emphasized that the embodiments of the invention asdescribed herein are intended to be illustrative only.

For example, the Fibre Channel interface used in the illustrativeembodiments may be replaced with another type of standard serial datachannel interface, or a non-standard serial data channel interface, aswell as combinations of standard and non-standard interfaces. As a moreparticular example, and as indicated previously herein, the techniquesof the present invention can be adapted in a straightforward manner foruse over other single-lane and multi-lane serial links including, butnot limited to Infini-Band, IEEE 1394, PCI-Express, Ethernet, andcertain DWDM or SONET links. As described above, in the illustrativeFibre Channel embodiments, four-character-long ordered sets designatedby a special control character are used to carry adaptive equalizationinformation. Other serial links may use other characters or frames tocarry such information, and such alternative arrangements are intendedto be encompassed by the term “ordered set” as used herein. Whatevermechanism is appropriate to a given serial link may be used in place ofthe particular ordered sets of the illustrative embodiments. Also, theparticular arrangements of system devices, command formats, and adaptiveequalization processes as shown in the figures may be varied inalternative embodiments. These and numerous other alternativeembodiments within the scope of the following claims will be readilyapparent to those skilled in the art.

1. An apparatus for use in a communication system having a plurality ofnodes, the apparatus comprising: a first node, the first node comprisinga transmitter configured for communication with a receiver of a secondnode and a receiver configured for communication with a transmitter ofthe second node; the first node being operative to receive from thesecond node information specifying an adjustment to one or moreequalization parameters of the first node; the information beingreceived in designated portions of one or more ordered sets transmittedfrom the second node to the first node in conjunction withinitialization of a communication link between the first and secondnodes; the first node being further operative to adjust the one or moreequalization parameters in accordance with the received information. 2.The apparatus of claim 1 wherein the one or more ordered sets compriseat least one training ordered set transmitted from the second node tothe first node during a speed negotiation process carried out betweenthe first node and the second node in conjunction with initialization ofthe communication link.
 3. The apparatus of claim 2 wherein the trainingordered set comprises a training pattern that is utilized by the secondnode in determining the information specifying an adjustment to one ormore equalization parameters of the first node.
 4. The apparatus ofclaim 2 wherein substantially simultaneous transmit adaptiveequalization is provided for both the first node and the second node,utilizing a plurality of training ordered sets transmitted between thefirst and second nodes during the speed negotiation process, eachtraining ordered set comprising a training pattern and equalizationparameter adjustment information.
 5. The apparatus of claim 1 whereinthe one or more ordered sets comprise at least first and second trainingordered sets, each of the first and second training ordered setscomprising a control character and a plurality of data portions, whereinthe information specifying an adjustment to one or more equalizationparameters of the first node is transmitted in particular bit positionsof one or more of the data portions of at least one of the trainingordered sets.
 6. The apparatus of claim 5 wherein a given one of thetraining ordered sets comprises an 8-bit control character and three8-bit data portions.
 7. The apparatus of claim 5 wherein the trainingordered sets are transmitted in place of one or more Not OperationalState (NOS) and Offline State (OLS) ordered sets which would otherwisebe transmitted between the first and second nodes during the speednegotiation process.
 8. The apparatus of claim 5 wherein the trainingordered sets are configured to communicate one or more status indicatorsfor a transmit adaptive equalization process carried out between thefirst and second nodes.
 9. The apparatus of claim 8 wherein the statusindicators comprise an in process indicator and a process completedindicator.
 10. The apparatus of claim 1 wherein the first node iscoupled to the second node via a bidirectional serial data channel. 11.The apparatus of claim 1 wherein the first node is configured tocommunicate with the second node over a Fibre Channel link.
 12. Theapparatus of claim 1 wherein the second node evaluates signal quality ofa signal transmitted by the transmitter of the first node, anddetermines the information specifying the adjustment to the one or moreequalization parameters based on the signal quality evaluation.
 13. Theapparatus of claim 1 wherein a transmit adaptive equalization processcomprising transmitting a signal and receiving information specifying anadjustment to one or more equalization parameters is repeated untilsignal quality of a given transmitted signal as received at the secondnode is determined to meet one or more designated criteria.
 14. Theapparatus of claim 1 wherein the one or more equalization parameterscomprise a plurality of tap coefficients of a filter associated with thetransmitter of the first node.
 15. The apparatus of claim 14 wherein thefilter comprises a finite impulse response filter.
 16. The apparatus ofclaim 1 wherein the information specifying an adjustment to one or moreequalization parameters of the transmitter of the first node comprisesfor a particular one of a plurality of coefficients at least one of anincrement coefficient action, a decrement coefficient action, and a holdcoefficient action.
 17. The apparatus of claim 1 wherein the informationspecifying an adjustment to one or more equalization parameters of thefirst node is transmitted with a training pattern, utilizing an orderedset format compatible with the Fibre Channel standard.
 18. The apparatusof claim 1 wherein the information specifying an adjustment to one ormore equalization parameters of the first node is transmitted utilizinga proxy mechanism in which the information is transmitted over at leastone additional interface other than those associated with first andsecond ends of the communication link.
 19. The apparatus of claim 1wherein the first node is implemented at least in part as an integratedcircuit.
 20. An integrated circuit for use in a communication systemhaving a plurality of nodes, the integrated circuit implementing atleast a portion of a first node, the first node comprising a transmitterconfigured for communication with a receiver of a second node and areceiver configured for communication with a transmitter of the secondnode, the first node being operative to receive from the second nodeinformation specifying an adjustment to one or more equalizationparameters of the first node, the information being received indesignated portions of one or more ordered sets transmitted from thesecond node to the first node in conjunction with initialization of acommunication link between the first and second nodes, and to adjust theone or more equalization parameters in accordance with the receivedinformation.
 21. A method for use in a communication system having aplurality of nodes, including at least a first node comprising atransmitter configured for communication with a receiver of a secondnode and a receiver configured for communication with a transmitter ofthe second node, the method comprising the steps of: receiving in thefirst node from the second node information specifying an adjustment toone or more equalization parameters of the first node, the informationbeing received in designated portions of one or more ordered setstransmitted from the second node to the first node in conjunction withinitialization of a communication link between the first and secondnodes; and adjusting the one or more equalization parameters inaccordance with the received information.
 22. An article of manufacturecomprising a machine-readable storage medium having one or more softwareprograms stored therein, for use in a communication system having aplurality of nodes, including at least a first node comprising atransmitter configured for communication with a receiver of a secondnode and a receiver configured for communication with a transmitter ofthe second node, the first node being operative under control of the oneor more software programs to perform the steps of: receiving from thesecond node information specifying an adjustment to one or moreequalization parameters of the first node, the information beingreceived in designated portions of one or more ordered sets transmittedfrom the second node to the first node in conjunction withinitialization of a communication link between the first and secondnodes; and adjusting the one or more equalization parameters inaccordance with the received information.